The purpose of this investigation is to characterize the effects of aging and age-related hearing loss on the central auditory representation of speech. Whereas much is known about the effects of age and hearing loss on the peripheral auditory system (ear), less is known about the effects of age and hearing loss on the central auditory system (brain) where sounds are integrated into meaningful events. Hearing aids and cochlear implants help compensate for disorders of the ear, but successful rehabilitation also depends on the brain's ability to learn and retain new acoustic cues representing auditory information. The present study compares neural representation of voice-onset-time (VOT) in young and elderly listeners, with and without hearing loss, using neurophysiological as well as behavioral measures. Comparing neural representation of speech in young and elderly listeners will help determine if "older" auditory systems are capable of representing fine-grained temporal speech cues as well as "younger" auditory systems. If a link between perception and neurophysiology can be made, then this research may help explain of why many aging adults do not always receive benefit from hearing aids or cochlear implants. It is hypothesized that aging and hearing loss may differentially alter the neural representation of speech cues in the central auditory system, which may in turn contribute to performance variability. The N1-P2 complex and mismatch negativity (MMN) are passively elicited event-related potentials (ERPs) that will be used to reflect neural representation of VOT in the central auditory system. Both the Nl-P2 complex and MMN have been shown to reflect both acoustic and phonemic representation of speech- sounds. Specifically, this study will determine whether aging, cochlear hearing loss and their interaction influence event- related-potentials (ERPs) elicited by changes in voice-onset-time (VOT). Also, the relationship between each subject's ERPs and each subject's ability to discriminate speech sounds on the basis of VOT will be examined.